i thought about this myself and was thinking that if u had a large subwoofer and played a a continuous beat with a very low frequency (possibly lower than we can hear) that the air fluctucation back and fourth could work in the same way as a fan to make plants grow stronger.
not saying that this would work any better or worse than a fan but was thinkin that it was technically a way that playing music could help ur plants grow, but i guess it wouldnt actually be music....
oh well, wat u think?